The present invention relates to semiconductors, and, more particularly, to method and apparatus for generating exposure data of use in a design pattern of a semiconductor integrated circuit on an exposure medium.
FIG. 1 is a schematic diagram of an electron beam (EB) exposure apparatus. The EB exposure apparatus has a stencil mask (or block mask) 12 and a plate 11 having a rectangular opening 13. As shown in FIG. 2, the stencil mask 12 has a plurality of first transmission apertures 14 having rectangular shapes, and a plurality of block areas 15.
Second transmission apertures 16 are formed in some block areas 15, and third transmission apertures 17 are formed in the other block areas 15. The second transmission apertures 16 take the shapes of "recursive patterns" which are acquired by extracting common portions from layout pattern data of LSI circuits. The recursive patterns include plural kinds of patterns. The block areas 15 in which the second transmission apertures 16 are formed are called "recursive blocks". The third transmission apertures 17 take the shapes of predetermined "segmental patterns" including oblique sides. That is, segmental patterns include oblique sides corresponding to the size of the block areas 15. The block areas 15 in which the third transmission apertures 17 are formed are called "segmental blocks".
Referring again to FIG. 1, an electron beam 10 is deflected by a first electromagnetic deflector 19 before passing the plate 11. The electron beam 10 is then deflected by a second electromagnetic deflector 20 before passing any one of the first to third transmission apertures 14-17 of the stencil mask 12. Accordingly, the cross-sectional shape of the electron beam 10 or the shape of its exposure pattern is changed. The electron beam 10 after it has passed the stencil mask 12 is further deflected by a third electromagnetic deflector 21. As a platform or stage 22 is moved along the X and Y axes, a desired pattern is exposed on a predetermined area of a wafer 23 located on the stage 22.
The size of a rectangular pattern exposed on the wafer 23 is determined by adjusting the degree of overlapping of the beam passing through the plate 11 with the associated first transmission aperture 14. This exposure scheme is called a variable rectangular system. As the electron beam 10 passes any second transmission aperture 16, the associated recursive pattern is exposed by a single shot. In a block exposure scheme using "recursive blocks", the third electromagnetic deflector 21 and the stage 22 are controlled to expose recursive patterns of the same shape on a plurality of areas of the wafer 23. As this block exposure involves fewer shots, the exposure time is decreased. In a block exposure scheme using "segmental blocks", as an electron beam passes any third transmission aperture 17, the associated segmental pattern is exposed by a single shot. Combining some segmental patterns permit a pattern of a desired shape to be exposed on the wafer.
As shown in FIG. 3A, in a case where the variable rectangular system is used to expose a pattern with an oblique side 24, on a wafer 23, for example, the pattern is formed by shooting a plurality of rectangular patterns 25 at a time. This scheme however increases the number of shots and elongates the exposure time. Further, this scheme exposes the oblique side 24 of the pattern in a stepwise form. To make the oblique side 24 as straight a line as possible, the rectangular patterns 25 constituting the pattern should have relatively narrow widths. This approach would result in an undesirable increase in the number of rectangular patterns 25 or the number of shots.
FIG. 3B shows a pattern formed by combining triangular patterns 26a and 26b and rectangular patterns 27a and 27b to improve the linearity of the oblique side 24 of the pattern. The triangular patterns 26a and 26b are formed by the third transmission aperture 17 formed in the stencil mask 12. The third transmission aperture 17 has a right-triangular shape including an oblique side which has the same inclination as the oblique side 24 of the pattern. The pattern can be formed with fewer shots than is required by the scheme in FIG. 3A by individually shooting the triangular patterns 26a and 26b and the rectangular patterns 27a and 27b. The triangular pattern 26b having a relatively small size is obtained by adjusting the degree of overlapping of the beam 10, which has passed the plate 11, with the associated third transmission aperture 17. The rectangular patterns 27a and 27b are obtained by adjusting the degree of overlapping of the beam 10, which has passed the plate 11, with the associated first transmission aperture 14.
An exposure data generating apparatus receives layout pattern data from a CAD system (not shown) and performs a graphics process on the layout pattern data. The graphics process includes a sizing process, a shrinking process and a rounding process which converts the coordinates of the layout pattern data to the grids (coordinates) of data the exposure apparatus handles. The exposure data generating apparatus then determines if exposure using the layout patterns on the stencil mask 12 is possible. Exposable layout patterns include, for example, a rectangular pattern 29a in FIG. 4A, right-triangular patterns 29b to 29e in FIG. 4B, parallelogram patterns 29f to 2i in FIGS. 4C and 4D, trapezoidal patterns 29j to 29n in FIGS. 4E and 4F and the patterns of the third transmission apertures 17 shown in FIG. 2. When exposure is possible, the exposure data generating apparatus converts the format of the layout pattern data to an adequate format for the exposure apparatus.
Patterns that cannot be exposed using the patterns on the stencil mask 12 are layout patterns which do not include horizontal and/or vertical sides. The exposure data generating apparatus segments such layout pattern data to produce plural pieces of rectangular pattern data. The exposure data generating apparatus then performs format conversion on the plural pieces of rectangular pattern data and supplies the converted rectangular pattern data to the exposure apparatus. The exposure apparatus carries out divided shot exposure using a plurality of rectangular patterns instead of the patterns on the stencil mask 12.
Depending on the shapes of the layout pattern, the layout pattern data after the graphics process may differ from the layout pattern data before the graphics process. This difference or error leads to an incoincidence between the coordinates of the layout pattern data before processing (format conversion) and the coordinates of the layout pattern data after processing. This leads to a probable case where although the original layout pattern is exposable using the patterns on the stencil mask 12, exposure is actually conducted using plural pieces of rectangular pattern data. This increases the number of shots by the exposure apparatus, increasing the exposure time for a single wafer. Particularly, specific triangular layout patterns excluding triangles having one angle of approximately 45 degrees are likely to be affected by the error. That is, since the graphics process may cause the inclination of the oblique side of a triangle to be varied by the error, the pattern data of the third transmission apertures 17 previously prepared cannot be used for such a specific triangular layout pattern. Therefore, exposure is executed using plural pieces of rectangular pattern data in place of the pattern data of the third transmission apertures 17. This results in an increased number of shots by the exposure apparatus.
Accordingly, it is an objective of the present invention to provide an efficient exposure data generating method and apparatus capable of decreasing the exposure time.